Light-emitting devices operating by principles of electroluminescence are used in many light-emitting structures, ranging from simple panel lights to complex displays and lasers, which cover the lighting industry, computer monitors, automotive industry, television and other consumer electronics, as well as military applications. Such light-emitting devices, of which light-emitting diodes (LED's) are exemplary, are tailored to emit visible light of a given wavelength by selection of its constituent compound semiconductor. For example, aluminum gallium arsenide is used for fabricating red LED's, gallium aluminum phosphide for fabricating green LED's, and gallium nitride for fabricating blue LED's. Multi-color light-emitting structures based upon such LED's are difficult to produce by conventional methods. Specifically, such diverse compounds are difficult to combine into an integral structure. Moreover, performance characteristics, such as current and voltage requirements, differ significantly for such diverse LED's and presents a circuitry challenge in the production of multi-color light-emitting structures.
Light-emitting devices typically incorporate a semiconductor phosphor layer that provides the light emission when biased. Wide band gap semiconductors (WBGS), such as gallium nitride, doped with light-emitting elements having partially-filled inner shells, such as rare earths (RE) and transition metals, are particularly attractive materials for the fabrication of such phosphor layers. Specifically, the emission efficiency of WGBS increases with band gap value, which facilitates room temperature operation.
Gallium nitride represents one of a number of Group III nitride semiconductor compounds that possess certain advantages when compared with other WBGS. For example, gallium nitride exhibits a direct band gap transition, excellent mechanical, chemical, and thermal stabilities, and an ability to incorporate large concentrations of luminescent centers. In addition, gallium nitride has a relatively large energy band gap (approximately 3.4 eV) that permits visible light emission from higher energy transitions, while still affording a measure of control over the conductivity.
Therefore, there is a need for light-emitting devices fabricated by MOCVD in which the light-emitting element is supplied by in-situ doping and in which the visible light emission is sufficiently intense for device applications.